From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6F9FB47799B; Tue, 16 Jun 2026 16:03:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781625825; cv=none; b=u0KEcCKFhmofmGvTGB/kdRxlN4UEg1L3M+j3+gd3MnznPmm/sUmWEnp3BW54ROIomhG4ZWDd/aIt+Em5PZ03Fv/GuyRXjAg5roIZEPC/PaikriMiO1E1aQCxqdJ+R7el2TZpdnXwt9Yin0C2t6xPEGYVZEqVC2F5BqEVj/mPjdA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781625825; c=relaxed/simple; bh=XYR14RqGd9hYjbLlJvHEiPsGgq4TQMNIfvTIGYBUClg=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=h1BLLojNwKn09cYhb2ndGZChFCGL/1NnUuRao0/ykoAoRpY1lMGXtahLG9zD9Aksnxe5zpNr1TjpWABCy6dS8HMUy1yvDzM8sM6OJxOGtWr+95fWf3gJsd3j8X2APt7iaIh0Ens5qmFwoc2+Nrpq7zPTJfoHBPnZYcfT6SMzfzw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=eSwq4/vG; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="eSwq4/vG" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 23F391F000E9; Tue, 16 Jun 2026 16:03:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1781625824; bh=AwGpj3tXZdTf1drTq5BOXIUMkcoOhI2UIZKqihn/Yug=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=eSwq4/vGUd4IWdwiCvlH1htCDe9jK5ep60E/Zz4ILHRhTOXMq3gkl+IBJfLOLbk3Z Dhf7qrU+0GC2+59TiG/9q4dUhIM9hHRmW0/b3Ib5y14BGJHIxhthgTnJWn/WZu9/qQ nuRceDDrFdkLnLkiktPpum3eHrROR2PCNwfsw5WA= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, SeongJae Park , Fernand Sieber , Leonard Foerster , Shakeel Butt , Andrew Morton Subject: [PATCH 6.18 184/325] mm/damon/ops-common: call folio_test_lru() after folio_get() Date: Tue, 16 Jun 2026 20:29:40 +0530 Message-ID: <20260616145107.056842127@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260616145057.827196531@linuxfoundation.org> References: <20260616145057.827196531@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: SeongJae Park commit d6b8b02a27b3dd09ec12144322b3dac46d9bc9ef upstream. damon_get_folio() speculatively calls folio_test_lru() before folio_try_get(). The folio can get freed and reallocated to a tail page. In the case, VM_BUG_ON_PGFLAGS() in const_folio_flags() can be triggered. Remove the speculative call. Also mark folio_test_lru() check right after folio_try_get() success as no more unlikely. The race should be rare. Also the problem can happen only if the kernel has enabled CONFIG_DEBUG_VM_PGFLAGS. No real world report of this issue has been made so far. This fix is based on only theoretical analysis. That said, a bug is a bug. A similar issue was also fixed via commit 3203b3ab0fcf ("mm/filemap: don't call folio_test_locked() without a reference in next_uptodate_folio()"). I don't expect this change will make a meaningful impact to DAMON performance in the real world, though I will be happy to be corrected from the real world reports. The issue was discovered [1] by Sashiko. Link: https://lore.kernel.org/20260525162256.8317-1-sj@kernel.org Link: https://lore.kernel.org/20260517234112.89245-1-sj@kernel.org [1] Fixes: 3f49584b262c ("mm/damon: implement primitives for the virtual memory address spaces") Signed-off-by: SeongJae Park Cc: Fernand Sieber Cc: Leonard Foerster Cc: Shakeel Butt Cc: # 5.15.x Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- mm/damon/ops-common.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) --- a/mm/damon/ops-common.c +++ b/mm/damon/ops-common.c @@ -32,9 +32,9 @@ struct folio *damon_get_folio(unsigned l return NULL; folio = page_folio(page); - if (!folio_test_lru(folio) || !folio_try_get(folio)) + if (!folio_try_get(folio)) return NULL; - if (unlikely(page_folio(page) != folio || !folio_test_lru(folio))) { + if (unlikely(page_folio(page) != folio) || !folio_test_lru(folio)) { folio_put(folio); folio = NULL; }